To reserve application flexibilities of integrated circuit chips in various conditions, many chips are designed to include one or several bonding option pads for receiving an external control voltage. By providing different control voltages to the pad via bonding wires, the chip is allowed to operate at different operating modes. Take a video processing chip as an example. By connecting a built-in bonding option pad to a power supply or ground, the chip may be set to receive video signals of different specifications. In practice, the bonding option pad may also be utilized to switch on or off specific functions in the chip for customization.
As shown in FIGS. 1A and 1B, the bonding option pad is usually fixed to an internal voltage supply or ground of the chip via a resistor R, so as to prevent the bonding option pad from entering a floating state. Take FIG. 1A as an example. A pad 10 may not correctly receive an external voltage when the pad 10 is damaged or a bonding wire 12 connecting to the pad 12 is disengaged, nevertheless, a voltage at a connecting point between the pad 10 and the internal circuit is at least maintained at a high level instead of being in the floating state. Conversely, under conditions that the pad 10, the bonding wire 12 and the external voltage supply 14 are all correctly connected, the voltage of the pad 10 is approximately equal to the voltage of the external voltage supply 14.
It is necessary that a chip manufacturer carries out various tests on a manufactured chip, and the tests generally include whether operating conditions of the bonding option pad and connections of the bonding option pad and the external voltage supply are normal. Take FIG. 1A as an example, a tester may first determine whether the pad 10 is functional before the bonding wire 12 is connected to the pad 10. After the bonding wire 12 is connected to the pad, the chip is again tested to determine whether connections between the pad 10, the bonding wire 12 and the external voltage supply 14 are correct.
With reference to FIG. 1A, before the bonding wire 12 is connected to the pad 10, the pad 10 is determined defective supposing the test staff finds that the voltage of the pad 10 is not at a high level, such that the chip is determined as a bad die. Furthermore, after connecting the pad 10 to the external voltage supply 14 via the bonding wire 12, supposing a test result indicates that the pad 10 is at a high level when in fact the external voltage supply 14 is connected to ground, it is inferred that the bonding wire 12 connected to the pad 10 is disengaged, such that the chip is also determined as a bad die.
In the absence of the resistor R, the connecting point of the internal circuit connected to the pad 10 enters the floating state when the above damages or incorrect electrical connections occur; that is, the voltage at the connecting point may either be at a high level or a low level. Take FIG. 1A as an example, an error condition cannot be reflected by a test result when the external voltage supply 14 is connected to ground and the floating point is happened to be at a low level. Therefore, the presence of the resistor R is essential.
However, when the external voltage supply 14 in FIG. 1A is connected to ground, the resistor R consumes a certain amount of power during normal operations. Similarly, the resistor R also consumes a certain amount of power during normal operations when the external voltage supply 14 in FIG. 1B is a power supply. In a field of mobile devices that highly values power lasting capabilities, the fixed power consumption brings rather significant undesirable effects.
From testing perspectives, the connections adopted in FIG. 1A and FIG. 1B cannot provide complete test correctness. Take the connection in FIG. 1A for example, under a testing mode after the bonding wire 12 is connected to the pad 10, when the external voltage supply 14 is connected to a power supply, the pad 10 remains at a high level for the resistor R is connected to an internal power supply VDD even if the bonding wire 12 is disengaged, such that the occurrence of an error condition eludes from the test result and probable issues during a welding process of the bonding wire 12 cannot be improved in time. Similarly, as shown in FIG. 1B, under the testing mode after the bonding wire 12 is connected to the pad 10, when the external voltage supply 14 is connected to ground, the pad 10 remains at a low level for the resistor R is connected to internal ground GND even if the bonding wire 12 is disengaged, such that the occurrence of an error condition also eludes from the test result.